In what he called “a provocative and defiant act,” President Obama charged on Tuesday that Russian President Vladimir Putin has started letting his calls go directly to voice mail.

Speaking at the White House before this week’s NATO summit, a visibly furious Obama said that Putin’s new practice of letting his calls go straight to voice mail “hampers our ability to discuss the future of Ukraine and other important issues going forward.”

Having left dozens of voice mails for the Russian President, Obama said that he tried to reach him via e-mail on Monday night but received an out-of-office auto reply.

“Given what he has been up to in Ukraine over the past few weeks, I find it impossible believe he has been out of the office,” Obama said.

The President hinted that Putin’s failure to respond to his voice mails could result in additional sanctions and signaled that he did not intend to call the Russian President again.“I have left my last voice mail for him,” he said, adding that the last time he called Putin his mailbox was full.